This invention relates to tools for use with dental prophylaxis angles, and in particular, to a prophylaxis cup which will provide a better seal with the angle to prevent abrasive and other foreign material from entering the angle.
Prophylaxis (prophy) cups are used by dentists or dental hygienists to polish a patient's teeth with paste carried by the rotating cup. The cup is mounted on the driven gear of a prophylaxis (prophy) angle. The prophy angle includes a body having a head carrying the driven gear and a tubular part carrying a drive gear including a shaft. The tubular body of the prophy angle is held on the nose of a motorized handpiece, and the drive shaft is gripped by a rotatable collet in the handpiece.
If the abrasive polishing paste or other foreign material enters the angle during a cleaning procedure, it can cause premature wear of the gears and their bearings. Moreover, mixtures of abrasive paste and saliva are difficult to clean out of the angle, and unless the angle is properly autoclaved it is a potential source of cross contamination.
To prevent foreign matter from entering the angle, most angles include an internal seal. When the seal wears, however, internal contamination of the angle occurs and expensive repairs are required. An alternative approach was suggested by George Richmond in a series of patents (U.S. Pat. Nos. 3,407,502, 3,436,830, 3,478,433, and 4,292,027) which disclose using the rubber prophy cup itself as the seal. This approach assures that a new seal is formed every time a new cup is placed on the prophy angle to perform a dental prophylaxis procedure. As shown in U.S. Pat. No. 3,478,433, it is possible to make a cup which forms a first seal with a knife edge at the end of a sleeve portion of a cap on the prophy angle, a second seal with a side of the sleeve portion, and a third seal (or slinger) with a peripheral portion of the cap. A commercial embodiment of such a sealing prophy cup is sold by Young Dental Manufacturing Company of Earth City, Mo., under the registered trademark TRIPLE SEAL. This cup is shown in FIG. 1 of the drawings. The cup 1 seals against the stem 3 of the angle's cap 5 at two points S1 and S2. Seal point S1 is a compression seal between the cup and the knife edge of the cap stem 3. As the cup 1 rotates, the knife edge cuts into the rubber cup and compresses the rubber outwardly. Seal point S2 is a ring seal which is formed by an inwardly directed annular rib 7 which seals against the side of the stem. A slinger or skirt 9 forms the third seal and functions to direct contaminants away from the opening in the cap 5.
The cup 1 has been found to work quite well. However, the multiple rubbing seals with the cap stem produce a large amount of friction. This friction causes the cup and prophy angle to heat up quickly and requires a greater amount of torque to run the cup than would be needed if the frictional engagements were reduced. Further, when shearing forces are applied to the cup, such as when the cup is pulled across a patient's tooth, the cup bends laterally. The bending of the cup causes the rib 7 and the seals S1 and S2 to pull away from the stem. This tends to break the seals and allow liquids and abrasives to enter the handpiece.